Supply Chain Management Journal

Aspects of Wireless Communications Use in Public Transportation Ionel PETRESCU Maria - Claudia SURUGIU Polytechnic University of Bucharest [email protected] [email protected] Abstract The information regarding road conditions and traffic, availability of parking spaces, etc. are distributed by public authorities in order to improve transportation efficiency, safety and environmental quality. Because data accuracy regarding position frequently depends how often the data is transmitted from the vehicle to the dispatch center and because there are a limited number of radio frequencies available in many urban areas, many transportation organizations have chosen as a strategy of transmission data reporting on important moments. In this case, each vehicle reports its position to dispatch center exclusively in fixed points or when the vehicle has exceeded the limit of timetable imposed set. The reporting system requires that each vehicle to know its position at a time, and planned position, in which would have to be, at that time. The most used transmission methods of buses position are "polling” and data reporting through wireless communication in exceptional cases. Despite the substantial benefits on which brings the use of AVL technology, only a very small number of transport companies use up huge amount of information that this system is recording. By implementing techniques that use a significantly higher amount of data, the transport companies should improve their performance in terms of developing a better work schedule (timetable), efficiency of services and ability to interact with customers. Key Words: RDS/TMC - Radio Data System/Traffic Message Channel, wireless communications, AVL (Automatic Vehicle Location) technology. Introduction. General notions about wireless networks Increasing popularity of wireless networks has led to a rapid decrease in the price of wireless devices along with a marked improvement in their technical performance. Today a wireless infrastructure can be achieved with much lower costs than a traditional cable. Next, reference will be made to the technologies of wireless networks, data transmission, and wireless protocols family standardized 802.11 (802.11a, 802.11b and 802.11g), known in many area as Wi-Fi (Wireless Fidelity) and 802.16 known as WiMAX (Worldwide Interoperability for Microwave Access), [IEEE 2008]. - IEEE 802.11b was ratified on 16 September 1999 and is probably the most popular wireless networking protocol used

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today. Uses DSSS modulation type (Direct Sequence Spread Spectrum). Operates in the frequency ISM (Industry Science Medicine), licenses are not required as long as they use standardized equipment. The limitations are: power output of up to 1 watt and only modulations of a kind with spread spectrum between 2.412 and 2.484 GHz; - 802.11g was applied in June 2003. Despite the late start, this protocol is currently the standard protocol in which wireless networks because it is implemented with virtually all wireless laptops and most other portable devices. Use the same sub-band frequency of ISM band as 802.11b, but uses the type of modulation OFDM (Orthogonal Frequency Division Multiplexing). Maximum data transfer speed is 54 Mbps, 25 Mbps with practical implementations. Data transfer can down to 11 Mbps or even lower values,

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passing the DSSS modulation type, to achieve compatibility with the more popular 802.11b protocol; - 802.11a. It was approved by IEEE on 16 September 1999. Uses modulation type OFDM. It has a maximum speed of 54 Mbps with implementations of up to 27 Mbps. Operating in the band between 5.745 and 5.805 GHz ISM band and UNII (Unlicensed National Information Infrastructure) between 5170 and 5320 GHz. This makes it incompatible with 802.11b or 802.11g. Higher frequency used corresponds to a lower frequency at the same power output subintervals although the spectrum is used more freely in comparison with the frequency around 2.4 GHz in some areas of the world, using these frequencies is not legal. Using a device based on this protocol can be made out only after consultation with local authorities. Therefore, equipment with the 802.11a protocol, although they are cheap, is not nearly as popular then those with 802.11b / g, (IEEE, 2008); - 802.16. It was approved in 2004 and can use multiple frequency bands, licensed and unlicensed, allocated by the ITU (International Telecommunication Union): two licensed bands: 3.3 to 3.8 GHz and 2.3 to 2.7 GHz; unlicensed band: 5.725 to 5.85 GHz; Flexibility on the use of Wi MAX spectrum, creating attractive conditions for implementing pricing, a variety of services: Telephony (VoIP Voice over Internet Protocol VoIP), video surveillance, consultation, remote monitoring, eLearning, enterprise, ad hoc networks; and users and a gradual expansion in all geographical areas. The same network can simultaneously support public services and private partnerships and provide favorable financial market competition IT & C services. WiMAX networks are capable of connectivity fixed, portable and mobile wireless broadband on the same network. WiMAX technology provides Internet access at speeds of 75 Mbps, the distance between relay stations can be up to 30 km and the area covered by an access point can have a radius of about 2 Km (Wireless Networking în the Developing World, 2006),(IEEE 2008).

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2. Wireless applications in public transport The traveler information technologies allow them to receive informations from on road and transport network. Most travel information is obtained using surveillance equipment (vehicle detectors, cameras, automatic vehicle location) and is processed by computers in a transportation management center and distributed through audio and video technologies. All system data are transmitted by wireless technology and radio communication. Radio technology provides greater flexibility making communication with both fixed and mobile users. Data communication for public transport is different from that for private transport. The public transport communication is personalized, meaning that non-standard protocol is used only for that application. Therefore different technologies have been implemented radio data transmission for transport as CDPD (Cellular Digital Packet Data), RDS (Radio Data System), TMC (Traffic Message Channel), each selling advantages and disadvantages. In public transport, communications are already used in many applications. Technology APTS (Advanced Public Transport System for advanced public transportation systems) and "intelligent vehicle" requires integrated communications functions, such as (Minea, Surugiu, 2007): • interaction between bus and control center; • access lanes to high occupancy vehicles or express buses transport; • priority traffic signals; • multimodal interfaces; • information on multimodal transport; • Information on the vehicle. To avoid overloading the network is used interrogation methods "polling." The "polling" method means individual buses access by the dispatcher’s computer, asking the position. This method requires that the installed system on the bus to be able to read and calculate its position. The bus position is then transmitted by radio

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dispatcher. Once all the buses were questioned about their position, the computer restarts buses questioning, duration of such cycle depending on the number of radio channels used. This length of time depends on the number of buses that are polled. The most companies that use this system request bus position at fixed time intervals. In case of unforeseen events, each bus sends its position to dispatcher only in some specified locations, or when the delay has not fit in the scales of tolerance (Sharon, 2003). Exceptional reporting makes more efficient the using of available radio channels, which is often a rare commodity. The data transmitted by the vehicles in transit are treated by the software's CAD (computer assisted dispatch) that allows the received information, and thus we refer to the status, location, road maintenance program, driver and incidents that have occurred on the road, to be displayed on the dispatcher computer’s screen. CAD software realizes the communications too, it assists the dispatcher in making operational decisions, and it archives data for other needs of the company. The communication data for public transport (RATB) is different from that for private transport (private cars). For public transportation the communication is personalized, that means that is used a non-standard protocol used only for the application. In terms of data transmitted, in each station is a panel with messages, to inform travelers, that display the current location of the bus station and the estimated time until it reaches the station. There are displaying only the buses which should reach, who have not passed the current station (where the panel). That way, they could achieve and various statistics that means, each bus arrived at each station at what time and how it is stayed, there can identify areas and periods of traffic congestion, etc. It can add other information on the panel. Regarding the transmission of messages may illustrate three approaches: 1. Each mode of transport to be a communication hub, which

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corresponds to mobile ad hoc networks; 2. Each station will be a node, so the routes of RATB become fixed channels of communication; 3. A mixed approach and given that buses and stations are equipped with transceivers; For drivers (excluding RATB) the most important information in city should be available the parking and congestion prevention providing alternative routes. Further information would be the weather and those with roads closed / blocked temporarily for work, etc. To ensure compatibility between communication devices would be best to use a standardized communication. A solution would be WLAN 802.11 that you can connect with mobile and laptop. At various points in the city are mounted access points so that it covered the whole city area. It forms a private network without having to provide access to the Internet, an intranet as the city expanded in size. There must be a server that connects users to information; they are available on any web browser. Also what do is to write application that retrieves and delivers information. The link between the vehicle and the control center, however, require in most cases, cover a large area for a city, which requires a service authorization (Campus Network Sesign Fundamental, 2006). Requirement for communication between vehicle and control center could be achieved through radio broadcasting services that can replace many dedicated communications direct links. The spectrum for a specific FM broadcast stations is greater than that required for an audio jump issued and the excess spectrum available for transmission of other services. APTS information can be superimposed on the usual transmissible by conventional commercial FM radio stations and other transmitters to the same type (eg advanced information system than by radio for highways and wireless data transmission system (RDS)). Features that require detailed information such as security and warning messages and guiding services on the

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route may require the existence of a special communications link. In this case, public transport can turn to alternative telecommunications techniques. Alternative communication techniques: • cell phone analog / digital - cellular telephone services covering most conventional part of the metropolitan area but is approaching the saturation level; • RDS with under carrying FM traffic information and other information can be transmitted by the sidebands of commercial FM radio stations; • Personal communications - are still under development but will allow communications in any area; • Communications with broad spectrum communications systems with broad spectrum transmit a low power signal, the information to be transmitted is distributed in a frequency band. To decode the transmitted information using a "smart receiver”; • shared-spectrum communications – co-existence in shared-spectrum communications of a few users of public information regarding safety which it not related to transport, through using digital sampling; • communications via satellite in low earth orbit; 2.1 The fleet management The management system of park of vehicles contains the technologies APTS (Advanced Public Transportation System) located in the vehicle and innovative solutions for planning, organizing and operating more efficient vehicles and fleet vehicles (Minea, Surugiu, 2007). Management of park focuses on vehicles, improving efficiency and safety of services provided to passengers. If transportation becomes more efficient and safer, he could become more attractive to passengers. Innovative technologies and solutions used are as follows: • Communication Systems; • Geographical information systems;

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• • • •

Automatic vehicle location; Automatic passenger counting; Software for transport operations; Treatment priorities at traffic signals.

2.2. Tracking system of traffic in realtime An example of such a system is used in public transport, providing information on vehicle, traffic, routes, whether passengers or dispatchers, they will always have access to accurate information regarding traffic. The update information is made in fractions of seconds, and the system is built as a network of intelligent nodes, communicating with the vehicles through a patented radio message system. The mode of decentralized access leads to a rapid, reliable and redundant system. The automatic vehicle location system AVL (Automatic Vehicle Location) is based on real-time determination of the geographical position of the vehicle and transmitting information to a central station. Each AVL system uses one or more of the following technologies of location: • rout calculation; • radio stations placed on the ground; • post signs and odometer; • global positioning system (GPS – Global Positioning System) The determining of the route is an autonomous form of vehicle location. With this technology, the bus determines its own position without the help of foreign technology (Figure 1.). There is communicate the starting point to the bus and then this measures distances from that point, on the odometer reading and driving direction. Because of the need for frequent measurement equipment setup compared to a known geographic position, this technology is rarely used alone. Usually, the measuring equipment is used to calculate a route together with the other technologies, such as placing signs at strategic positions on the route, or the GPS. The channel signalling system is based on a series of beacons placed along the bus route. The beacons emit a low

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power signal that is detected by a receiver mounted in the vehicle. The vehicle forwards the position to dispatching center, depending on the distance (obtained from the odometer) that has undergone the last bus station signal. Another strategy is to channel signal bus to receive signals and transmit this information to the dispatch center. AVL system is a configuration by type client – server, the information is collected in large servers, processed in real time and offered to the client through a simple Web-based interface. The client access to appropriate information is secure. With location information, and data is also transmitted on the state of motion (parking, speed, etc.) and interface for FM 4100, data from the vehicle's onboard computer via digital

interface device included in the CAN (fuel level, weight axles, etc.) as vehicle equipment in accordance with the sensors (Minea, Surugiu, 2007). • Control and monitor transport; • Detailed route of vehicle; • Communication with drivers via SMS; • Helps to increase fleet productivity; • Prevents cheating on working time; • Allows for better management of labor; • Real-time tracking of cargo route; • Ability to use Microsoft Map Point or other maps; • Enables efficient planning of transport routes; • You can easily identify what is carried in tractor trailer.

Figure. 1. Vehicle location system

The communication system on the vehicle consists essentially of a radio modem or wireless transceiver according to the

technique used and a microcontroller or microprocessor for processing.

Figure 2. Radio communication at the vehicle

Source: Sharon, 2003

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During the day, program compliance and other relevant information will be automatically displayed continuously using a computer board. Being connected with all subsystems on board, including electrical systems, onboard computers will help the driver with useful information for driving. Passengers will have access to real-time traffic information via the onboard electronic displays and voice announcements. Data transfer to the vehicle consists of hourly new, voice files, advertisements, videos, etc.., downloaded via communication System in the core, which can use both wireless technologies, as well as W LAN. 2.3 Traffic Planning A system used in traffic planning should be integrated with all major brands traffic planning system on the market, the standard import functions are available for specific data formats to integrate them fully in the planning of the recipient. The Traffic Planning System provides traffic planners a powerful computer support for management, scheduling and vehicle dispatching activities. Feedback from the Statistics System can be used to evaluate performance and to streamline the transport activity. Features: - Graphical planning schedules; - Review links; - Park planning optimisation; - Advanced calendar functions; - Automatic generation of schedules. Passengers can plan their itinerary via the Internet at an information kiosk or calling a specialized service. The travel planner can be integrated with other systems in real time and can be taken into account in real-time traffic situations to assess optimal route. Even if the usual connection is canceled or delayed, the travel planner will always suggest the best alternative. The travel planner is developed using the latest technology and uses a super fast search engine to present the shortest time to reach the optimal route to your destination.

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-

Features fast and efficient; integrates information in real time easy to use interface graphical presentation Open platform

2.4 Traffic Management The entire fleet is monitored in real time, the application providing a comprehensive overview on the location, the compliance program and the status of all connected vehicle tracking system in real-time traffic. You can control the entire fleet management from a standard laptop with software installed and an Internet connection. It is also possible to monitor the technical condition of each vehicle by accessing the multiplex electrical system (Springer, 2006). This means that the dispatcher has access to the same information as the driver of the vehicle: speed of the vehicle, door signs, oil pressure, fuel level, temperature, alarm and many more. Features: - verify whether in time of + / 1 second; - vehicle diagnostic; - vehicle positioning with a map of possibilities for increasing the areas; - messages from and to vehicles; - alarm signal. Advanced Traffic Management System (ATMS - Advanced Traffic Management System) is a transport management system and is based on a complex infrastructure, which includes sensors (for circulation, weather conditions, visibility, radio and electro magnetic interference), cameras are video and data transmission network (optical fiber, cable modem and wireless links) and accurate position determination equipment (GPS Global Positioning System), (Krazit, 2006). The main technologies used mainly in such systems ATMS are: • vehicle detector; • traffic light systems that meet traffic demand; • Traffic cameras supervises; • variable message signs; • telephone information systems for passengers traffic; • Radio information system for passengers

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(TARS – Traveler Advisory Radio System). The system form a network with mobile and fixed nodes, equipped with transceivers, similar with wireless sensor networks. The fixed nodes are located in transportation stations, on the poles on the bus route and on the control center, and the mobile nodes are located on bus. Due to use in cities, the buildings are an important attenuation ratio and it is necessary that at some distance to place relay nodes, followed by public transportation routes, communication distance is of the order of up to a few hundred meters. Nodes act as communication station, detection, data processing and control displaying data. The fixed nodes are placed in known locations, their position being marked on maps at the electronic traffic control centers. The position of mobile nodes, ID_route

ID_sender

ID_receiver

Where the fields are: ID_route is the control centre identifier, ID_sender is the transmitter identifier, ID_receiver is the receiver identifier, code is a message code, and in this case is 0. The message code is depending on the type of the message. Because of the large variety of types of messages a list of codes cannot be displayed. The message field contains the message itself, in this case is the number of nodes through which the message relay. Message format remain identical for all messages. 2.5 Monitoring of the vehicle The vehicles on the road transmit periodically a message consisting of its identifier and the direction, tour or return. The message is intercepted by nodes in the transmission range, but it is processed only by the node placed on his direction. The ID_receiver and ID_route fields are 0, the other fields are filled in properly. The node that receives the message, add to it

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placed on vehicles can be estimated at any time according to fixed nodes. The system presented is based on the realtime localization of the vehicles at any moment; each vehicle has the position between some two stations on a bus route. Each node has a unique identifier. Nodes contained in the interim and stations have the format of the identifier of the category to which they belong, the bus route and a number. For example for the class identifier station is St, and for intermediate relay nodes is IP. The bus route must specify the direction of the vehicle, tour or return, because the nodes on both sides of the road can intercept the message transmitted by a vehicle. The message is addressed only to nodes on receivers for his path and must be processed only by them. The message format is: Code

message

its identifier, and then forward it to the next node until arrived to the control center. ID_receiver and ID_route fields are filled out only by the fixed nodes according to the associated path. The route of transmission to the control center is known. In Figure 3 is the principle of vehicle monitoring. The vehicle transmits a message having fields in the figure. Station St.4.2 receives and sends it to the nearest control Centre. Content of the message means that the station St.4.2 detect vehicle V.4.33, located on line 4 with the number 33, tour direction at 17: 15. The messages arrived at the control center, are decoded in accordance with table 1 and estimate the location of the vehicle, in real time, as being somewhere near the St.4.2 station. The position is used to update the road map in real time, monitoring of vehicles, traffic optimization, statistics, etc.

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Figure. 3. The principle of vehicle monitoring

Conclusion Unlike other radio systems, Wi-Fi uses a radio spectrum license is not needed so you do not require approval for use. It allows the development of wireless local area networks without using wires, reducing costs of network development and avoiding various obstacles in the implementation of the network (inaccessible places that can not be wired). Intranet system forms a network protocol stack and can use TCP / IP, resulting in easy integration with the Internet and can be connected with it to exchange data with other systems of transport (marine, air, rail) transport in order to fluidize and passenger and therefore reduce waiting times. Sensor networks are reliable, accurate, flexible, involves low costs are easier to build and why they are used in many fields. The main results of the study can materialize in the following: • Wireless sensor systems are principles with the aim to minimize road travel time if the average waiting time at traffic lights is minimal; • Wireless sensor networks provide a benefit that the ability to work in a multi tasking, with both dual role in the transmission of traffic

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information to the access point and store statistical data collected during operation cycle. A useful result in double benefit of improving the system worked. The application can add up the existing systems, providing solutions for data transmission in the cities. Due to the fact that it is a decentralized system, selforganized, the number of administrative messages is reduced, giving an extra bandwidth to the data transmission. This results in a more efficient use of channel of communication, allowing you to transfer more data. The system is more flexible than the Intelligent Traffic Control System using RFID presented in (Chandra, 2009) and improves the functionality of the system presented in (X. Yang, 2003). References A. Chandra, A. Chattaraj and S. Bansal (2009), An Intelligent Traffic Control System using RFID, IEEE Potentials, 28, 3, pp. 40-43, Campus Network Sesign Fundamental (2006), copyright, Cisco Press; Don Torrieri, Springer, (2005) ”Principles of Spread - Spectrum Communication Systems”, Boston; IEEE Standard for Information Technology (2008) — Telecommunications and information exchange between systems —

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Local and metropolitan area networks — Specific requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, http://standards.ieee.org; KRAZIT TOM, (2006) - Faster WI-FI standard gets draft approval, CNET News.com,; Maria Claudia Surugiu, Marius Minea, Florin Domnel Grafu (2007)- Sisteme inteligente de transport – aplicatii, ed. MATRIXROM, Bucuresti;

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Sharon E. (2003), Telecommunications Network Modeling, Planning and Design, London; Wireless Networking în the Developing World, Limehouse Book Sprint Team, 2006; X. Yang, Advanced public transport system in Singapore (2003), Intelligent Transportation Systems, 2, pp. 1660-1663

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